<!DOCTYPE html>
<html>
<head>
<style>

input { -moz-appearance: textfield; }

</style>
<script>

function boom()
{
    window.getComputedStyle(x, "::-moz-number-spin-down").getPropertyValue("color");
}

</script>
<body onload="boom();">
<input type="number" id="x">
</body>
</html>
